1. Field of the Invention
The invention relates to novel proteins and their genes from the cattle tick, Rhipicephalus microplus, and their use as vaccines to control and prevent tick infestations in treated livestock, including bovines, which protects them against the transmission of tick-borne pathogens.
2. Description of the Prior Art
The cattle tick (also referred to as the southern cattle tick), Rhipicephalus (Boophilus) microplus, was declared to be eradicated from the US by 1943 (Graham and Hourrigan, 1977. J. Med. Entomol. 13:629-658), and all cattle presented for importation at the Texas-Mexico border are treated with acaricides to prevent reintroduction. However, there is a risk of the reestablishment of this tick in the US due to the presence of acaricide-resistant populations in Mexico (Miller et al., 2005. J. Med. Entomol. 42:912-917). Rhipicephalus microplus is a vector for the protozoan agents causing cattle fever, Babesia bovis and Babesia bigemina. Since cattle fever is endemic in Mexico, and all imported cattle are checked only for ticks but not for infection with this parasite, there is a constant threat of the resumption of cattle fever transmission in the US. This threat has triggered the search for new, environmentally safe and effective techniques for control of R. microplus that can be integrated with conventional chemical control methods.
Anti-tick vaccines are a potential alternative to chemical control methods, but the tick-protective antigens identified thus far remain to be developed and marketed by private concerns for commercial use by livestock producers (de la Fuente and Kocan, 2006. Parasite Immunol. 28:275-283). Development of novel tick control strategies requires increased knowledge of the complement of proteins expressed in R. microplus. Three proteome studies have been published for R. microplus. Sequence information for 20 abundantly expressed larval proteins, representing multiple cuticular proteins, a cytoskeletal protein, a salivary gland-associated protein, several housekeeping proteins, and tropomyosin have been described (Untalan et al., 2005. Insect Biochem. Mol. Biol. 35:141-151). Nineteen membrane proteins were identified that were differentially expressed in the ovaries in uninfected and Babesia bovis-infected ticks. Ovarian proteins that were up-regulated in infected ticks included calreticulin, two myosin subunits, an endoplasmic reticulum protein, a peptidyl-prolyl cis-trans isomerase (PPIase), a cytochrome c oxidase subunit, a glutamine synthetase, and a family of Kunitz-type serine protease inhibitors. Among the down-regulated ovarian proteins were another PPIase, a hemoglobin subunit, and a lysozyme (Rachinsky et al., 2007. Insect Biochem. Mol. Biol. 37:1291-1308). More recently, Rachinsky et al. (2008. Vet. Parasit. 152:294-313) described an extensive survey of proteins in the midgut epithelium that were regulated in response to infection as part of an ongoing effort to establish a proteome database to be utilized to identify specific proteins that may be involved in successful pathogen transmission or tick feeding, and which could serve as candidates for tick control methods.
However, despite these and other advances, the need remains for improved techniques for control of the southern cattle tick.